1. Field of the Invention
The present invention relates to modified human hemoglobins having an oxygen binding affinity equal or less than natural human hemoglobin, a blood product containing the same, and vectors containing a DNA sequence coding for the modified human hemoglobins.
2. Description of Related Art
In human red cells, the interaction of 2,3-DPG with hemoglobin (hemoglobin Hb) regulates the efficient release of oxygen to the tissues (R. Benesch et al, Nature, 221, 618 (1969)). Bovine red cells do not contain appreciable amounts of 2,3-DPG (H. F. Bunn, Science, 172, 1049 (1971)), however, human and bovine erythrocytes have the same oxygen affinity, indicating that either bovine Hb has an intrinsically low oxygen affinity, or that the oxygen affinity of this Hb becomes physiologically acceptable through a different mechanism of regulation.
The present inventors have observed that, in the absence of organic and inorganic anions, the oxygen affinities of human and bovine Hbs are similar (C. Fronticelli et al, J. Biol. Chem., 259, 10841 (1984)), indicating that the low oxygen affinity of bovine Hb could not be an intrinsic property of the molecule. Furthermore, the present inventors have found that bovine Hb has a particular sensitivity to chlorides and, as a result, at physiological chloride concentration (0.1 M) it could attain oxygen affinity values lower than those measured for human Hb in the presence of 2,3-DPG (C. Fronticelli et al, J. Mol. Biol., 202, 343 (1988)). The data indicated that the enhanced sensitivity of bovine Hb to the solvent components was due to the presence of extra chloride-binding sites, absent in human Hb. The inventors have also discovered that bovine Hb could discriminate between the halides on the basis of the charge density of the molecules (C. Fronticelli et al, J. Mol. Biol., 202, 343 (1988)), as if the interaction of the protein with the anions was modulated by the hydrophobic characteristics of the protein.
The different functional characteristics and the different number of Cl binding sites of human and bovine Hbs must originate from the amino acid compositions of the two proteins.
The sequence of natural .beta.-chain of hemoglobin is as follows: ##STR1##
Mutant hemoglobin molecules are disclosed in PCT Publication International Publication No. WO 88/09179 which was published on Dec. 1, 1988, which is hereby incorporated by reference.